The site uses weight to work out the value for the 1st or 2nd class shipping / postage, but need this to stop when it reaches a certain cart value and is then shipped / posted at a set Tracked rate. This rate has been set and does appear as an option when the value is reached, but need it as the default with no weight based options. This was simple when using woocommerce when the site was on wordpress, but there does not appear to be any simple option for this in Shopify.